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linux/arch/x86/lib/insn-eval.c

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/*
* Utility functions for x86 operand and address decoding
*
* Copyright (C) Intel Corporation 2017
*/
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/ratelimit.h>
#include <linux/mmu_context.h>
#include <asm/desc_defs.h>
#include <asm/desc.h>
#include <asm/inat.h>
#include <asm/insn.h>
#include <asm/insn-eval.h>
#include <asm/ldt.h>
#include <asm/vm86.h>
#undef pr_fmt
#define pr_fmt(fmt) "insn: " fmt
enum reg_type {
REG_TYPE_RM = 0,
REG_TYPE_REG,
REG_TYPE_INDEX,
REG_TYPE_BASE,
};
/**
* is_string_insn() - Determine if instruction is a string instruction
* @insn: Instruction containing the opcode to inspect
*
* Returns:
*
* true if the instruction, determined by the opcode, is any of the
* string instructions as defined in the Intel Software Development manual.
* False otherwise.
*/
static bool is_string_insn(struct insn *insn)
{
insn_get_opcode(insn);
/* All string instructions have a 1-byte opcode. */
if (insn->opcode.nbytes != 1)
return false;
switch (insn->opcode.bytes[0]) {
case 0x6c ... 0x6f: /* INS, OUTS */
case 0xa4 ... 0xa7: /* MOVS, CMPS */
case 0xaa ... 0xaf: /* STOS, LODS, SCAS */
return true;
default:
return false;
}
}
/**
* insn_has_rep_prefix() - Determine if instruction has a REP prefix
* @insn: Instruction containing the prefix to inspect
*
* Returns:
*
* true if the instruction has a REP prefix, false if not.
*/
bool insn_has_rep_prefix(struct insn *insn)
{
int i;
insn_get_prefixes(insn);
for (i = 0; i < insn->prefixes.nbytes; i++) {
insn_byte_t p = insn->prefixes.bytes[i];
if (p == 0xf2 || p == 0xf3)
return true;
}
return false;
}
/**
* get_seg_reg_override_idx() - obtain segment register override index
* @insn: Valid instruction with segment override prefixes
*
* Inspect the instruction prefixes in @insn and find segment overrides, if any.
*
* Returns:
*
* A constant identifying the segment register to use, among CS, SS, DS,
* ES, FS, or GS. INAT_SEG_REG_DEFAULT is returned if no segment override
* prefixes were found.
*
* -EINVAL in case of error.
*/
static int get_seg_reg_override_idx(struct insn *insn)
{
int idx = INAT_SEG_REG_DEFAULT;
int num_overrides = 0, i;
insn_get_prefixes(insn);
/* Look for any segment override prefixes. */
for (i = 0; i < insn->prefixes.nbytes; i++) {
insn_attr_t attr;
attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]);
switch (attr) {
case INAT_MAKE_PREFIX(INAT_PFX_CS):
idx = INAT_SEG_REG_CS;
num_overrides++;
break;
case INAT_MAKE_PREFIX(INAT_PFX_SS):
idx = INAT_SEG_REG_SS;
num_overrides++;
break;
case INAT_MAKE_PREFIX(INAT_PFX_DS):
idx = INAT_SEG_REG_DS;
num_overrides++;
break;
case INAT_MAKE_PREFIX(INAT_PFX_ES):
idx = INAT_SEG_REG_ES;
num_overrides++;
break;
case INAT_MAKE_PREFIX(INAT_PFX_FS):
idx = INAT_SEG_REG_FS;
num_overrides++;
break;
case INAT_MAKE_PREFIX(INAT_PFX_GS):
idx = INAT_SEG_REG_GS;
num_overrides++;
break;
/* No default action needed. */
}
}
/* More than one segment override prefix leads to undefined behavior. */
if (num_overrides > 1)
return -EINVAL;
return idx;
}
/**
* check_seg_overrides() - check if segment override prefixes are allowed
* @insn: Valid instruction with segment override prefixes
* @regoff: Operand offset, in pt_regs, for which the check is performed
*
* For a particular register used in register-indirect addressing, determine if
* segment override prefixes can be used. Specifically, no overrides are allowed
* for rDI if used with a string instruction.
*
* Returns:
*
* True if segment override prefixes can be used with the register indicated
* in @regoff. False if otherwise.
*/
static bool check_seg_overrides(struct insn *insn, int regoff)
{
if (regoff == offsetof(struct pt_regs, di) && is_string_insn(insn))
return false;
return true;
}
/**
* resolve_default_seg() - resolve default segment register index for an operand
* @insn: Instruction with opcode and address size. Must be valid.
* @regs: Register values as seen when entering kernel mode
* @off: Operand offset, in pt_regs, for which resolution is needed
*
* Resolve the default segment register index associated with the instruction
* operand register indicated by @off. Such index is resolved based on defaults
* described in the Intel Software Development Manual.
*
* Returns:
*
* If in protected mode, a constant identifying the segment register to use,
* among CS, SS, ES or DS. If in long mode, INAT_SEG_REG_IGNORE.
*
* -EINVAL in case of error.
*/
static int resolve_default_seg(struct insn *insn, struct pt_regs *regs, int off)
{
if (any_64bit_mode(regs))
return INAT_SEG_REG_IGNORE;
/*
* Resolve the default segment register as described in Section 3.7.4
* of the Intel Software Development Manual Vol. 1:
*
* + DS for all references involving r[ABCD]X, and rSI.
* + If used in a string instruction, ES for rDI. Otherwise, DS.
* + AX, CX and DX are not valid register operands in 16-bit address
* encodings but are valid for 32-bit and 64-bit encodings.
* + -EDOM is reserved to identify for cases in which no register
* is used (i.e., displacement-only addressing). Use DS.
* + SS for rSP or rBP.
* + CS for rIP.
*/
switch (off) {
case offsetof(struct pt_regs, ax):
case offsetof(struct pt_regs, cx):
case offsetof(struct pt_regs, dx):
/* Need insn to verify address size. */
if (insn->addr_bytes == 2)
return -EINVAL;
fallthrough;
case -EDOM:
case offsetof(struct pt_regs, bx):
case offsetof(struct pt_regs, si):
return INAT_SEG_REG_DS;
case offsetof(struct pt_regs, di):
if (is_string_insn(insn))
return INAT_SEG_REG_ES;
return INAT_SEG_REG_DS;
case offsetof(struct pt_regs, bp):
case offsetof(struct pt_regs, sp):
return INAT_SEG_REG_SS;
case offsetof(struct pt_regs, ip):
return INAT_SEG_REG_CS;
default:
return -EINVAL;
}
}
/**
* resolve_seg_reg() - obtain segment register index
* @insn: Instruction with operands
* @regs: Register values as seen when entering kernel mode
* @regoff: Operand offset, in pt_regs, used to deterimine segment register
*
* Determine the segment register associated with the operands and, if
* applicable, prefixes and the instruction pointed by @insn.
*
* The segment register associated to an operand used in register-indirect
* addressing depends on:
*
* a) Whether running in long mode (in such a case segments are ignored, except
* if FS or GS are used).
*
* b) Whether segment override prefixes can be used. Certain instructions and
* registers do not allow override prefixes.
*
* c) Whether segment overrides prefixes are found in the instruction prefixes.
*
* d) If there are not segment override prefixes or they cannot be used, the
* default segment register associated with the operand register is used.
*
* The function checks first if segment override prefixes can be used with the
* operand indicated by @regoff. If allowed, obtain such overridden segment
* register index. Lastly, if not prefixes were found or cannot be used, resolve
* the segment register index to use based on the defaults described in the
* Intel documentation. In long mode, all segment register indexes will be
* ignored, except if overrides were found for FS or GS. All these operations
* are done using helper functions.
*
* The operand register, @regoff, is represented as the offset from the base of
* pt_regs.
*
* As stated, the main use of this function is to determine the segment register
* index based on the instruction, its operands and prefixes. Hence, @insn
* must be valid. However, if @regoff indicates rIP, we don't need to inspect
* @insn at all as in this case CS is used in all cases. This case is checked
* before proceeding further.
*
* Please note that this function does not return the value in the segment
* register (i.e., the segment selector) but our defined index. The segment
* selector needs to be obtained using get_segment_selector() and passing the
* segment register index resolved by this function.
*
* Returns:
*
* An index identifying the segment register to use, among CS, SS, DS,
* ES, FS, or GS. INAT_SEG_REG_IGNORE is returned if running in long mode.
*
* -EINVAL in case of error.
*/
static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff)
{
int idx;
/*
* In the unlikely event of having to resolve the segment register
* index for rIP, do it first. Segment override prefixes should not
* be used. Hence, it is not necessary to inspect the instruction,
* which may be invalid at this point.
*/
if (regoff == offsetof(struct pt_regs, ip)) {
if (any_64bit_mode(regs))
return INAT_SEG_REG_IGNORE;
else
return INAT_SEG_REG_CS;
}
if (!insn)
return -EINVAL;
if (!check_seg_overrides(insn, regoff))
return resolve_default_seg(insn, regs, regoff);
idx = get_seg_reg_override_idx(insn);
if (idx < 0)
return idx;
if (idx == INAT_SEG_REG_DEFAULT)
return resolve_default_seg(insn, regs, regoff);
/*
* In long mode, segment override prefixes are ignored, except for
* overrides for FS and GS.
*/
if (any_64bit_mode(regs)) {
if (idx != INAT_SEG_REG_FS &&
idx != INAT_SEG_REG_GS)
idx = INAT_SEG_REG_IGNORE;
}
return idx;
}
/**
* get_segment_selector() - obtain segment selector
* @regs: Register values as seen when entering kernel mode
* @seg_reg_idx: Segment register index to use
*
* Obtain the segment selector from any of the CS, SS, DS, ES, FS, GS segment
* registers. In CONFIG_X86_32, the segment is obtained from either pt_regs or
* kernel_vm86_regs as applicable. In CONFIG_X86_64, CS and SS are obtained
* from pt_regs. DS, ES, FS and GS are obtained by reading the actual CPU
* registers. This done for only for completeness as in CONFIG_X86_64 segment
* registers are ignored.
*
* Returns:
*
* Value of the segment selector, including null when running in
* long mode.
*
* -EINVAL on error.
*/
static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx)
{
#ifdef CONFIG_X86_64
unsigned short sel;
switch (seg_reg_idx) {
case INAT_SEG_REG_IGNORE:
return 0;
case INAT_SEG_REG_CS:
return (unsigned short)(regs->cs & 0xffff);
case INAT_SEG_REG_SS:
return (unsigned short)(regs->ss & 0xffff);
case INAT_SEG_REG_DS:
savesegment(ds, sel);
return sel;
case INAT_SEG_REG_ES:
savesegment(es, sel);
return sel;
case INAT_SEG_REG_FS:
savesegment(fs, sel);
return sel;
case INAT_SEG_REG_GS:
savesegment(gs, sel);
return sel;
default:
return -EINVAL;
}
#else /* CONFIG_X86_32 */
struct kernel_vm86_regs *vm86regs = (struct kernel_vm86_regs *)regs;
if (v8086_mode(regs)) {
switch (seg_reg_idx) {
case INAT_SEG_REG_CS:
return (unsigned short)(regs->cs & 0xffff);
case INAT_SEG_REG_SS:
return (unsigned short)(regs->ss & 0xffff);
case INAT_SEG_REG_DS:
return vm86regs->ds;
case INAT_SEG_REG_ES:
return vm86regs->es;
case INAT_SEG_REG_FS:
return vm86regs->fs;
case INAT_SEG_REG_GS:
return vm86regs->gs;
case INAT_SEG_REG_IGNORE:
default:
return -EINVAL;
}
}
switch (seg_reg_idx) {
case INAT_SEG_REG_CS:
return (unsigned short)(regs->cs & 0xffff);
case INAT_SEG_REG_SS:
return (unsigned short)(regs->ss & 0xffff);
case INAT_SEG_REG_DS:
return (unsigned short)(regs->ds & 0xffff);
case INAT_SEG_REG_ES:
return (unsigned short)(regs->es & 0xffff);
case INAT_SEG_REG_FS:
return (unsigned short)(regs->fs & 0xffff);
case INAT_SEG_REG_GS:
/*
* GS may or may not be in regs as per CONFIG_X86_32_LAZY_GS.
* The macro below takes care of both cases.
*/
return get_user_gs(regs);
case INAT_SEG_REG_IGNORE:
default:
return -EINVAL;
}
#endif /* CONFIG_X86_64 */
}
static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
enum reg_type type)
{
int regno = 0;
static const int regoff[] = {
offsetof(struct pt_regs, ax),
offsetof(struct pt_regs, cx),
offsetof(struct pt_regs, dx),
offsetof(struct pt_regs, bx),
offsetof(struct pt_regs, sp),
offsetof(struct pt_regs, bp),
offsetof(struct pt_regs, si),
offsetof(struct pt_regs, di),
#ifdef CONFIG_X86_64
offsetof(struct pt_regs, r8),
offsetof(struct pt_regs, r9),
offsetof(struct pt_regs, r10),
offsetof(struct pt_regs, r11),
offsetof(struct pt_regs, r12),
offsetof(struct pt_regs, r13),
offsetof(struct pt_regs, r14),
offsetof(struct pt_regs, r15),
#endif
};
int nr_registers = ARRAY_SIZE(regoff);
/*
* Don't possibly decode a 32-bit instructions as
* reading a 64-bit-only register.
*/
if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64)
nr_registers -= 8;
switch (type) {
case REG_TYPE_RM:
regno = X86_MODRM_RM(insn->modrm.value);
/*
* ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement
* follows the ModRM byte.
*/
if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5)
return -EDOM;
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
case REG_TYPE_REG:
regno = X86_MODRM_REG(insn->modrm.value);
if (X86_REX_R(insn->rex_prefix.value))
regno += 8;
break;
case REG_TYPE_INDEX:
regno = X86_SIB_INDEX(insn->sib.value);
if (X86_REX_X(insn->rex_prefix.value))
regno += 8;
/*
* If ModRM.mod != 3 and SIB.index = 4 the scale*index
* portion of the address computation is null. This is
* true only if REX.X is 0. In such a case, the SIB index
* is used in the address computation.
*/
if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4)
return -EDOM;
break;
case REG_TYPE_BASE:
regno = X86_SIB_BASE(insn->sib.value);
/*
* If ModRM.mod is 0 and SIB.base == 5, the base of the
* register-indirect addressing is 0. In this case, a
* 32-bit displacement follows the SIB byte.
*/
if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5)
return -EDOM;
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
default:
pr_err_ratelimited("invalid register type: %d\n", type);
return -EINVAL;
}
if (regno >= nr_registers) {
WARN_ONCE(1, "decoded an instruction with an invalid register");
return -EINVAL;
}
return regoff[regno];
}
/**
* get_reg_offset_16() - Obtain offset of register indicated by instruction
* @insn: Instruction containing ModRM byte
* @regs: Register values as seen when entering kernel mode
* @offs1: Offset of the first operand register
* @offs2: Offset of the second opeand register, if applicable
*
* Obtain the offset, in pt_regs, of the registers indicated by the ModRM byte
* in @insn. This function is to be used with 16-bit address encodings. The
* @offs1 and @offs2 will be written with the offset of the two registers
* indicated by the instruction. In cases where any of the registers is not
* referenced by the instruction, the value will be set to -EDOM.
*
* Returns:
*
* 0 on success, -EINVAL on error.
*/
static int get_reg_offset_16(struct insn *insn, struct pt_regs *regs,
int *offs1, int *offs2)
{
/*
* 16-bit addressing can use one or two registers. Specifics of
* encodings are given in Table 2-1. "16-Bit Addressing Forms with the
* ModR/M Byte" of the Intel Software Development Manual.
*/
static const int regoff1[] = {
offsetof(struct pt_regs, bx),
offsetof(struct pt_regs, bx),
offsetof(struct pt_regs, bp),
offsetof(struct pt_regs, bp),
offsetof(struct pt_regs, si),
offsetof(struct pt_regs, di),
offsetof(struct pt_regs, bp),
offsetof(struct pt_regs, bx),
};
static const int regoff2[] = {
offsetof(struct pt_regs, si),
offsetof(struct pt_regs, di),
offsetof(struct pt_regs, si),
offsetof(struct pt_regs, di),
-EDOM,
-EDOM,
-EDOM,
-EDOM,
};
if (!offs1 || !offs2)
return -EINVAL;
/* Operand is a register, use the generic function. */
if (X86_MODRM_MOD(insn->modrm.value) == 3) {
*offs1 = insn_get_modrm_rm_off(insn, regs);
*offs2 = -EDOM;
return 0;
}
*offs1 = regoff1[X86_MODRM_RM(insn->modrm.value)];
*offs2 = regoff2[X86_MODRM_RM(insn->modrm.value)];
/*
* If ModRM.mod is 0 and ModRM.rm is 110b, then we use displacement-
* only addressing. This means that no registers are involved in
* computing the effective address. Thus, ensure that the first
* register offset is invalild. The second register offset is already
* invalid under the aforementioned conditions.
*/
if ((X86_MODRM_MOD(insn->modrm.value) == 0) &&
(X86_MODRM_RM(insn->modrm.value) == 6))
*offs1 = -EDOM;
return 0;
}
/**
* get_desc() - Obtain contents of a segment descriptor
* @out: Segment descriptor contents on success
* @sel: Segment selector
*
* Given a segment selector, obtain a pointer to the segment descriptor.
* Both global and local descriptor tables are supported.
*
* Returns:
*
* True on success, false on failure.
*
* NULL on error.
*/
static bool get_desc(struct desc_struct *out, unsigned short sel)
{
struct desc_ptr gdt_desc = {0, 0};
unsigned long desc_base;
#ifdef CONFIG_MODIFY_LDT_SYSCALL
if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) {
bool success = false;
struct ldt_struct *ldt;
/* Bits [15:3] contain the index of the desired entry. */
sel >>= 3;
mutex_lock(&current->active_mm->context.lock);
ldt = current->active_mm->context.ldt;
if (ldt && sel < ldt->nr_entries) {
*out = ldt->entries[sel];
success = true;
}
mutex_unlock(&current->active_mm->context.lock);
return success;
}
#endif
native_store_gdt(&gdt_desc);
/*
* Segment descriptors have a size of 8 bytes. Thus, the index is
* multiplied by 8 to obtain the memory offset of the desired descriptor
* from the base of the GDT. As bits [15:3] of the segment selector
* contain the index, it can be regarded as multiplied by 8 already.
* All that remains is to clear bits [2:0].
*/
desc_base = sel & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK);
if (desc_base > gdt_desc.size)
return false;
*out = *(struct desc_struct *)(gdt_desc.address + desc_base);
return true;
}
/**
* insn_get_seg_base() - Obtain base address of segment descriptor.
* @regs: Register values as seen when entering kernel mode
* @seg_reg_idx: Index of the segment register pointing to seg descriptor
*
* Obtain the base address of the segment as indicated by the segment descriptor
* pointed by the segment selector. The segment selector is obtained from the
* input segment register index @seg_reg_idx.
*
* Returns:
*
* In protected mode, base address of the segment. Zero in long mode,
* except when FS or GS are used. In virtual-8086 mode, the segment
* selector shifted 4 bits to the right.
*
* -1L in case of error.
*/
unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx)
{
struct desc_struct desc;
short sel;
sel = get_segment_selector(regs, seg_reg_idx);
if (sel < 0)
return -1L;
if (v8086_mode(regs))
/*
* Base is simply the segment selector shifted 4
* bits to the right.
*/
return (unsigned long)(sel << 4);
if (any_64bit_mode(regs)) {
/*
* Only FS or GS will have a base address, the rest of
* the segments' bases are forced to 0.
*/
unsigned long base;
if (seg_reg_idx == INAT_SEG_REG_FS) {
rdmsrl(MSR_FS_BASE, base);
} else if (seg_reg_idx == INAT_SEG_REG_GS) {
/*
* swapgs was called at the kernel entry point. Thus,
* MSR_KERNEL_GS_BASE will have the user-space GS base.
*/
if (user_mode(regs))
rdmsrl(MSR_KERNEL_GS_BASE, base);
else
rdmsrl(MSR_GS_BASE, base);
} else {
base = 0;
}
return base;
}
/* In protected mode the segment selector cannot be null. */
if (!sel)
return -1L;
if (!get_desc(&desc, sel))
return -1L;
return get_desc_base(&desc);
}
/**
* get_seg_limit() - Obtain the limit of a segment descriptor
* @regs: Register values as seen when entering kernel mode
* @seg_reg_idx: Index of the segment register pointing to seg descriptor
*
* Obtain the limit of the segment as indicated by the segment descriptor
* pointed by the segment selector. The segment selector is obtained from the
* input segment register index @seg_reg_idx.
*
* Returns:
*
* In protected mode, the limit of the segment descriptor in bytes.
* In long mode and virtual-8086 mode, segment limits are not enforced. Thus,
* limit is returned as -1L to imply a limit-less segment.
*
* Zero is returned on error.
*/
static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx)
{
struct desc_struct desc;
unsigned long limit;
short sel;
sel = get_segment_selector(regs, seg_reg_idx);
if (sel < 0)
return 0;
if (any_64bit_mode(regs) || v8086_mode(regs))
return -1L;
if (!sel)
return 0;
if (!get_desc(&desc, sel))
return 0;
/*
* If the granularity bit is set, the limit is given in multiples
* of 4096. This also means that the 12 least significant bits are
* not tested when checking the segment limits. In practice,
* this means that the segment ends in (limit << 12) + 0xfff.
*/
limit = get_desc_limit(&desc);
if (desc.g)
limit = (limit << 12) + 0xfff;
return limit;
}
/**
* insn_get_code_seg_params() - Obtain code segment parameters
* @regs: Structure with register values as seen when entering kernel mode
*
* Obtain address and operand sizes of the code segment. It is obtained from the
* selector contained in the CS register in regs. In protected mode, the default
* address is determined by inspecting the L and D bits of the segment
* descriptor. In virtual-8086 mode, the default is always two bytes for both
* address and operand sizes.
*
* Returns:
*
* An int containing ORed-in default parameters on success.
*
* -EINVAL on error.
*/
int insn_get_code_seg_params(struct pt_regs *regs)
{
struct desc_struct desc;
short sel;
if (v8086_mode(regs))
/* Address and operand size are both 16-bit. */
return INSN_CODE_SEG_PARAMS(2, 2);
sel = get_segment_selector(regs, INAT_SEG_REG_CS);
if (sel < 0)
return sel;
if (!get_desc(&desc, sel))
return -EINVAL;
/*
* The most significant byte of the Type field of the segment descriptor
* determines whether a segment contains data or code. If this is a data
* segment, return error.
*/
if (!(desc.type & BIT(3)))
return -EINVAL;
switch ((desc.l << 1) | desc.d) {
case 0: /*
* Legacy mode. CS.L=0, CS.D=0. Address and operand size are
* both 16-bit.
*/
return INSN_CODE_SEG_PARAMS(2, 2);
case 1: /*
* Legacy mode. CS.L=0, CS.D=1. Address and operand size are
* both 32-bit.
*/
return INSN_CODE_SEG_PARAMS(4, 4);
case 2: /*
* IA-32e 64-bit mode. CS.L=1, CS.D=0. Address size is 64-bit;
* operand size is 32-bit.
*/
return INSN_CODE_SEG_PARAMS(4, 8);
case 3: /* Invalid setting. CS.L=1, CS.D=1 */
fallthrough;
default:
return -EINVAL;
}
}
/**
* insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte
* @insn: Instruction containing the ModRM byte
* @regs: Register values as seen when entering kernel mode
*
* Returns:
*
* The register indicated by the r/m part of the ModRM byte. The
* register is obtained as an offset from the base of pt_regs. In specific
* cases, the returned value can be -EDOM to indicate that the particular value
* of ModRM does not refer to a register and shall be ignored.
*/
int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs)
{
return get_reg_offset(insn, regs, REG_TYPE_RM);
}
/**
* insn_get_modrm_reg_off() - Obtain register in reg part of the ModRM byte
* @insn: Instruction containing the ModRM byte
* @regs: Register values as seen when entering kernel mode
*
* Returns:
*
* The register indicated by the reg part of the ModRM byte. The
* register is obtained as an offset from the base of pt_regs.
*/
int insn_get_modrm_reg_off(struct insn *insn, struct pt_regs *regs)
{
return get_reg_offset(insn, regs, REG_TYPE_REG);
}
/**
* get_seg_base_limit() - obtain base address and limit of a segment
* @insn: Instruction. Must be valid.
* @regs: Register values as seen when entering kernel mode
* @regoff: Operand offset, in pt_regs, used to resolve segment descriptor
* @base: Obtained segment base
* @limit: Obtained segment limit
*
* Obtain the base address and limit of the segment associated with the operand
* @regoff and, if any or allowed, override prefixes in @insn. This function is
* different from insn_get_seg_base() as the latter does not resolve the segment
* associated with the instruction operand. If a limit is not needed (e.g.,
* when running in long mode), @limit can be NULL.
*
* Returns:
*
* 0 on success. @base and @limit will contain the base address and of the
* resolved segment, respectively.
*
* -EINVAL on error.
*/
static int get_seg_base_limit(struct insn *insn, struct pt_regs *regs,
int regoff, unsigned long *base,
unsigned long *limit)
{
int seg_reg_idx;
if (!base)
return -EINVAL;
seg_reg_idx = resolve_seg_reg(insn, regs, regoff);
if (seg_reg_idx < 0)
return seg_reg_idx;
*base = insn_get_seg_base(regs, seg_reg_idx);
if (*base == -1L)
return -EINVAL;
if (!limit)
return 0;
*limit = get_seg_limit(regs, seg_reg_idx);
if (!(*limit))
return -EINVAL;
return 0;
}
/**
* get_eff_addr_reg() - Obtain effective address from register operand
* @insn: Instruction. Must be valid.
* @regs: Register values as seen when entering kernel mode
* @regoff: Obtained operand offset, in pt_regs, with the effective address
* @eff_addr: Obtained effective address
*
* Obtain the effective address stored in the register operand as indicated by
* the ModRM byte. This function is to be used only with register addressing
* (i.e., ModRM.mod is 3). The effective address is saved in @eff_addr. The
* register operand, as an offset from the base of pt_regs, is saved in @regoff;
* such offset can then be used to resolve the segment associated with the
* operand. This function can be used with any of the supported address sizes
* in x86.
*
* Returns:
*
* 0 on success. @eff_addr will have the effective address stored in the
* operand indicated by ModRM. @regoff will have such operand as an offset from
* the base of pt_regs.
*
* -EINVAL on error.
*/
static int get_eff_addr_reg(struct insn *insn, struct pt_regs *regs,
int *regoff, long *eff_addr)
{
insn_get_modrm(insn);
if (!insn->modrm.nbytes)
return -EINVAL;
if (X86_MODRM_MOD(insn->modrm.value) != 3)
return -EINVAL;
*regoff = get_reg_offset(insn, regs, REG_TYPE_RM);
if (*regoff < 0)
return -EINVAL;
/* Ignore bytes that are outside the address size. */
if (insn->addr_bytes == 2)
*eff_addr = regs_get_register(regs, *regoff) & 0xffff;
else if (insn->addr_bytes == 4)
*eff_addr = regs_get_register(regs, *regoff) & 0xffffffff;
else /* 64-bit address */
*eff_addr = regs_get_register(regs, *regoff);
return 0;
}
/**
* get_eff_addr_modrm() - Obtain referenced effective address via ModRM
* @insn: Instruction. Must be valid.
* @regs: Register values as seen when entering kernel mode
* @regoff: Obtained operand offset, in pt_regs, associated with segment
* @eff_addr: Obtained effective address
*
* Obtain the effective address referenced by the ModRM byte of @insn. After
* identifying the registers involved in the register-indirect memory reference,
* its value is obtained from the operands in @regs. The computed address is
* stored @eff_addr. Also, the register operand that indicates the associated
* segment is stored in @regoff, this parameter can later be used to determine
* such segment.
*
* Returns:
*
* 0 on success. @eff_addr will have the referenced effective address. @regoff
* will have a register, as an offset from the base of pt_regs, that can be used
* to resolve the associated segment.
*
* -EINVAL on error.
*/
static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs,
int *regoff, long *eff_addr)
{
long tmp;
if (insn->addr_bytes != 8 && insn->addr_bytes != 4)
return -EINVAL;
insn_get_modrm(insn);
if (!insn->modrm.nbytes)
return -EINVAL;
if (X86_MODRM_MOD(insn->modrm.value) > 2)
return -EINVAL;
*regoff = get_reg_offset(insn, regs, REG_TYPE_RM);
/*
* -EDOM means that we must ignore the address_offset. In such a case,
* in 64-bit mode the effective address relative to the rIP of the
* following instruction.
*/
if (*regoff == -EDOM) {
if (any_64bit_mode(regs))
tmp = regs->ip + insn->length;
else
tmp = 0;
} else if (*regoff < 0) {
return -EINVAL;
} else {
tmp = regs_get_register(regs, *regoff);
}
if (insn->addr_bytes == 4) {
int addr32 = (int)(tmp & 0xffffffff) + insn->displacement.value;
*eff_addr = addr32 & 0xffffffff;
} else {
*eff_addr = tmp + insn->displacement.value;
}
return 0;
}
/**
* get_eff_addr_modrm_16() - Obtain referenced effective address via ModRM
* @insn: Instruction. Must be valid.
* @regs: Register values as seen when entering kernel mode
* @regoff: Obtained operand offset, in pt_regs, associated with segment
* @eff_addr: Obtained effective address
*
* Obtain the 16-bit effective address referenced by the ModRM byte of @insn.
* After identifying the registers involved in the register-indirect memory
* reference, its value is obtained from the operands in @regs. The computed
* address is stored @eff_addr. Also, the register operand that indicates
* the associated segment is stored in @regoff, this parameter can later be used
* to determine such segment.
*
* Returns:
*
* 0 on success. @eff_addr will have the referenced effective address. @regoff
* will have a register, as an offset from the base of pt_regs, that can be used
* to resolve the associated segment.
*
* -EINVAL on error.
*/
static int get_eff_addr_modrm_16(struct insn *insn, struct pt_regs *regs,
int *regoff, short *eff_addr)
{
int addr_offset1, addr_offset2, ret;
short addr1 = 0, addr2 = 0, displacement;
if (insn->addr_bytes != 2)
return -EINVAL;
insn_get_modrm(insn);
if (!insn->modrm.nbytes)
return -EINVAL;
if (X86_MODRM_MOD(insn->modrm.value) > 2)
return -EINVAL;
ret = get_reg_offset_16(insn, regs, &addr_offset1, &addr_offset2);
if (ret < 0)
return -EINVAL;
/*
* Don't fail on invalid offset values. They might be invalid because
* they cannot be used for this particular value of ModRM. Instead, use
* them in the computation only if they contain a valid value.
*/
if (addr_offset1 != -EDOM)
addr1 = regs_get_register(regs, addr_offset1) & 0xffff;
if (addr_offset2 != -EDOM)
addr2 = regs_get_register(regs, addr_offset2) & 0xffff;
displacement = insn->displacement.value & 0xffff;
*eff_addr = addr1 + addr2 + displacement;
/*
* The first operand register could indicate to use of either SS or DS
* registers to obtain the segment selector. The second operand
* register can only indicate the use of DS. Thus, the first operand
* will be used to obtain the segment selector.
*/
*regoff = addr_offset1;
return 0;
}
/**
* get_eff_addr_sib() - Obtain referenced effective address via SIB
* @insn: Instruction. Must be valid.
* @regs: Register values as seen when entering kernel mode
* @regoff: Obtained operand offset, in pt_regs, associated with segment
* @eff_addr: Obtained effective address
*
* Obtain the effective address referenced by the SIB byte of @insn. After
* identifying the registers involved in the indexed, register-indirect memory
* reference, its value is obtained from the operands in @regs. The computed
* address is stored @eff_addr. Also, the register operand that indicates the
* associated segment is stored in @regoff, this parameter can later be used to
* determine such segment.
*
* Returns:
*
* 0 on success. @eff_addr will have the referenced effective address.
* @base_offset will have a register, as an offset from the base of pt_regs,
* that can be used to resolve the associated segment.
*
* -EINVAL on error.
*/
static int get_eff_addr_sib(struct insn *insn, struct pt_regs *regs,
int *base_offset, long *eff_addr)
{
long base, indx;
int indx_offset;
if (insn->addr_bytes != 8 && insn->addr_bytes != 4)
return -EINVAL;
insn_get_modrm(insn);
if (!insn->modrm.nbytes)
return -EINVAL;
if (X86_MODRM_MOD(insn->modrm.value) > 2)
return -EINVAL;
insn_get_sib(insn);
if (!insn->sib.nbytes)
return -EINVAL;
*base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
/*
* Negative values in the base and index offset means an error when
* decoding the SIB byte. Except -EDOM, which means that the registers
* should not be used in the address computation.
*/
if (*base_offset == -EDOM)
base = 0;
else if (*base_offset < 0)
return -EINVAL;
else
base = regs_get_register(regs, *base_offset);
if (indx_offset == -EDOM)
indx = 0;
else if (indx_offset < 0)
return -EINVAL;
else
indx = regs_get_register(regs, indx_offset);
if (insn->addr_bytes == 4) {
int addr32, base32, idx32;
base32 = base & 0xffffffff;
idx32 = indx & 0xffffffff;
addr32 = base32 + idx32 * (1 << X86_SIB_SCALE(insn->sib.value));
addr32 += insn->displacement.value;
*eff_addr = addr32 & 0xffffffff;
} else {
*eff_addr = base + indx * (1 << X86_SIB_SCALE(insn->sib.value));
*eff_addr += insn->displacement.value;
}
return 0;
}
/**
* get_addr_ref_16() - Obtain the 16-bit address referred by instruction
* @insn: Instruction containing ModRM byte and displacement
* @regs: Register values as seen when entering kernel mode
*
* This function is to be used with 16-bit address encodings. Obtain the memory
* address referred by the instruction's ModRM and displacement bytes. Also, the
* segment used as base is determined by either any segment override prefixes in
* @insn or the default segment of the registers involved in the address
* computation. In protected mode, segment limits are enforced.
*
* Returns:
*
* Linear address referenced by the instruction operands on success.
*
* -1L on error.
*/
static void __user *get_addr_ref_16(struct insn *insn, struct pt_regs *regs)
{
unsigned long linear_addr = -1L, seg_base, seg_limit;
int ret, regoff;
short eff_addr;
long tmp;
insn_get_modrm(insn);
insn_get_displacement(insn);
if (insn->addr_bytes != 2)
goto out;
if (X86_MODRM_MOD(insn->modrm.value) == 3) {
ret = get_eff_addr_reg(insn, regs, &regoff, &tmp);
if (ret)
goto out;
eff_addr = tmp;
} else {
ret = get_eff_addr_modrm_16(insn, regs, &regoff, &eff_addr);
if (ret)
goto out;
}
ret = get_seg_base_limit(insn, regs, regoff, &seg_base, &seg_limit);
if (ret)
goto out;
/*
* Before computing the linear address, make sure the effective address
* is within the limits of the segment. In virtual-8086 mode, segment
* limits are not enforced. In such a case, the segment limit is -1L to
* reflect this fact.
*/
if ((unsigned long)(eff_addr & 0xffff) > seg_limit)
goto out;
linear_addr = (unsigned long)(eff_addr & 0xffff) + seg_base;
/* Limit linear address to 20 bits */
if (v8086_mode(regs))
linear_addr &= 0xfffff;
out:
return (void __user *)linear_addr;
}
/**
* get_addr_ref_32() - Obtain a 32-bit linear address
* @insn: Instruction with ModRM, SIB bytes and displacement
* @regs: Register values as seen when entering kernel mode
*
* This function is to be used with 32-bit address encodings to obtain the
* linear memory address referred by the instruction's ModRM, SIB,
* displacement bytes and segment base address, as applicable. If in protected
* mode, segment limits are enforced.
*
* Returns:
*
* Linear address referenced by instruction and registers on success.
*
* -1L on error.
*/
static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs)
{
unsigned long linear_addr = -1L, seg_base, seg_limit;
int eff_addr, regoff;
long tmp;
int ret;
if (insn->addr_bytes != 4)
goto out;
if (X86_MODRM_MOD(insn->modrm.value) == 3) {
ret = get_eff_addr_reg(insn, regs, &regoff, &tmp);
if (ret)
goto out;
eff_addr = tmp;
} else {
if (insn->sib.nbytes) {
ret = get_eff_addr_sib(insn, regs, &regoff, &tmp);
if (ret)
goto out;
eff_addr = tmp;
} else {
ret = get_eff_addr_modrm(insn, regs, &regoff, &tmp);
if (ret)
goto out;
eff_addr = tmp;
}
}
ret = get_seg_base_limit(insn, regs, regoff, &seg_base, &seg_limit);
if (ret)
goto out;
/*
* In protected mode, before computing the linear address, make sure
* the effective address is within the limits of the segment.
* 32-bit addresses can be used in long and virtual-8086 modes if an
* address override prefix is used. In such cases, segment limits are
* not enforced. When in virtual-8086 mode, the segment limit is -1L
* to reflect this situation.
*
* After computed, the effective address is treated as an unsigned
* quantity.
*/
if (!any_64bit_mode(regs) && ((unsigned int)eff_addr > seg_limit))
goto out;
/*
* Even though 32-bit address encodings are allowed in virtual-8086
* mode, the address range is still limited to [0x-0xffff].
*/
if (v8086_mode(regs) && (eff_addr & ~0xffff))
goto out;
/*
* Data type long could be 64 bits in size. Ensure that our 32-bit
* effective address is not sign-extended when computing the linear
* address.
*/
linear_addr = (unsigned long)(eff_addr & 0xffffffff) + seg_base;
/* Limit linear address to 20 bits */
if (v8086_mode(regs))
linear_addr &= 0xfffff;
out:
return (void __user *)linear_addr;
}
/**
* get_addr_ref_64() - Obtain a 64-bit linear address
* @insn: Instruction struct with ModRM and SIB bytes and displacement
* @regs: Structure with register values as seen when entering kernel mode
*
* This function is to be used with 64-bit address encodings to obtain the
* linear memory address referred by the instruction's ModRM, SIB,
* displacement bytes and segment base address, as applicable.
*
* Returns:
*
* Linear address referenced by instruction and registers on success.
*
* -1L on error.
*/
#ifndef CONFIG_X86_64
static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs)
{
return (void __user *)-1L;
}
#else
static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs)
{
unsigned long linear_addr = -1L, seg_base;
int regoff, ret;
long eff_addr;
if (insn->addr_bytes != 8)
goto out;
if (X86_MODRM_MOD(insn->modrm.value) == 3) {
ret = get_eff_addr_reg(insn, regs, &regoff, &eff_addr);
if (ret)
goto out;
} else {
if (insn->sib.nbytes) {
ret = get_eff_addr_sib(insn, regs, &regoff, &eff_addr);
if (ret)
goto out;
} else {
ret = get_eff_addr_modrm(insn, regs, &regoff, &eff_addr);
if (ret)
goto out;
}
}
ret = get_seg_base_limit(insn, regs, regoff, &seg_base, NULL);
if (ret)
goto out;
linear_addr = (unsigned long)eff_addr + seg_base;
out:
return (void __user *)linear_addr;
}
#endif /* CONFIG_X86_64 */
/**
* insn_get_addr_ref() - Obtain the linear address referred by instruction
* @insn: Instruction structure containing ModRM byte and displacement
* @regs: Structure with register values as seen when entering kernel mode
*
* Obtain the linear address referred by the instruction's ModRM, SIB and
* displacement bytes, and segment base, as applicable. In protected mode,
* segment limits are enforced.
*
* Returns:
*
* Linear address referenced by instruction and registers on success.
*
* -1L on error.
*/
void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
{
if (!insn || !regs)
return (void __user *)-1L;
switch (insn->addr_bytes) {
case 2:
return get_addr_ref_16(insn, regs);
case 4:
return get_addr_ref_32(insn, regs);
case 8:
return get_addr_ref_64(insn, regs);
default:
return (void __user *)-1L;
}
}
/**
* insn_fetch_from_user() - Copy instruction bytes from user-space memory
* @regs: Structure with register values as seen when entering kernel mode
* @buf: Array to store the fetched instruction
*
* Gets the linear address of the instruction and copies the instruction bytes
* to the buf.
*
* Returns:
*
* Number of instruction bytes copied.
*
* 0 if nothing was copied.
*/
int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
{
unsigned long seg_base = 0;
int not_copied;
/*
* If not in user-space long mode, a custom code segment could be in
* use. This is true in protected mode (if the process defined a local
* descriptor table), or virtual-8086 mode. In most of the cases
* seg_base will be zero as in USER_CS.
*/
if (!user_64bit_mode(regs)) {
seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS);
if (seg_base == -1L)
return 0;
}
not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip),
MAX_INSN_SIZE);
return MAX_INSN_SIZE - not_copied;
}
/**
* insn_decode() - Decode an instruction
* @insn: Structure to store decoded instruction
* @regs: Structure with register values as seen when entering kernel mode
* @buf: Buffer containing the instruction bytes
* @buf_size: Number of instruction bytes available in buf
*
* Decodes the instruction provided in buf and stores the decoding results in
* insn. Also determines the correct address and operand sizes.
*
* Returns:
*
* True if instruction was decoded, False otherwise.
*/
bool insn_decode(struct insn *insn, struct pt_regs *regs,
unsigned char buf[MAX_INSN_SIZE], int buf_size)
{
int seg_defs;
insn_init(insn, buf, buf_size, user_64bit_mode(regs));
/*
* Override the default operand and address sizes with what is specified
* in the code segment descriptor. The instruction decoder only sets
* the address size it to either 4 or 8 address bytes and does nothing
* for the operand bytes. This OK for most of the cases, but we could
* have special cases where, for instance, a 16-bit code segment
* descriptor is used.
* If there is an address override prefix, the instruction decoder
* correctly updates these values, even for 16-bit defaults.
*/
seg_defs = insn_get_code_seg_params(regs);
if (seg_defs == -EINVAL)
return false;
insn->addr_bytes = INSN_CODE_SEG_ADDR_SZ(seg_defs);
insn->opnd_bytes = INSN_CODE_SEG_OPND_SZ(seg_defs);
insn_get_length(insn);
if (buf_size < insn->length)
return false;
return true;
}
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